Re: [patch] net_sched: stack info leak in cbq_dump_wrr()

[walter harms <wharms@bfs.de>]

Am 30.07.2013 09:18, schrieb David Miller:
> From: Joe Perches <joe@perches.com>
> Date: Tue, 30 Jul 2013 00:12:32 -0700
> 
>> On Tue, 2013-07-30 at 09:55 +0300, Dan Carpenter wrote:
>>> On Mon, Jul 29, 2013 at 01:12:31PM -0700, Joe Perches wrote:
>>>> On Mon, 2013-07-29 at 23:01 +0300, Dan Carpenter wrote:
>>>>> On Mon, Jul 29, 2013 at 12:44:32PM -0700, Joe Perches wrote:
>>>>>> On Mon, 2013-07-29 at 22:36 +0300, Dan Carpenter wrote:
>>>>>>> opt.__reserved isn't cleared so we leak a byte of stack information.
>>>>>> []
>>>>>>> diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
>>>>>> []
>>>>>>> @@ -1469,6 +1469,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
>>>>>>>  	opt.allot = cl->allot;
>>>>>>>  	opt.priority = cl->priority + 1;
>>>>>>>  	opt.cpriority = cl->cpriority + 1;
>>>>>>> +	opt.__reserved = 0;
>>>>>>>  	opt.weight = cl->weight;
>>>>>>>  	if (nla_put(skb, TCA_CBQ_WRROPT, sizeof(opt), &opt))
>>>>>>>  		goto nla_put_failure;
>>>>>>
>>>>>> Alignment isn't guaranteed here so it'd
>>>>>> probably be better with a memset.
>>>>>>
>>>>>
>>>>> Hm...  Which arches would align it differently?
>>>>
>>>> Hey Dan.
>>>>
>>>> None so far as I know, but what difference does it make
>>>> when it's a general correctness issue?
>>>>
>>>
>>> Because I would assume if these aren't aligned the same way we have
>>> far more serious problems than just this one case.  It would change
>>> the user space API and break network protocols.
>>
>> <shrug>
>>
>> I didn't say it was necessary to be done here, I said it
>> was a correctness issue.  I still believe that's true.
>>
>> The nla_put here is by structure, the struct is unpacked,
>> and it's local to the arch, not a particular endian type.
>>
>> btw: to answer David's question, gcc 4.7 is smart enough
>> to elide resetting values when the struct is initialized
>> to 0 either with a memset or using {0}.
> 
> Ok, I've just commited the following, thanks everyone.
> 
> --------------------
>>From a0db856a95a29efb1c23db55c02d9f0ff4f0db48 Mon Sep 17 00:00:00 2001
> From: "David S. Miller" <davem@davemloft.net>
> Date: Tue, 30 Jul 2013 00:16:21 -0700
> Subject: [PATCH] net_sched: Fix stack info leak in cbq_dump_wrr().
> 
> Make sure the reserved fields, and padding (if any), are
> fully initialized.
> 
> Based upon a patch by Dan Carpenter and feedback from
> Joe Perches.
> 
> Signed-off-by: David S. Miller <davem@davemloft.net>
> ---
>  net/sched/sch_cbq.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
> index 71a5688..7a42c81 100644
> --- a/net/sched/sch_cbq.c
> +++ b/net/sched/sch_cbq.c
> @@ -1465,6 +1465,7 @@ static int cbq_dump_wrr(struct sk_buff *skb, struct cbq_class *cl)
>  	unsigned char *b = skb_tail_pointer(skb);
>  	struct tc_cbq_wrropt opt;
>  
> +	memset(&opt, 0, sizeof(opt));
>  	opt.flags = 0;
>  	opt.allot = cl->allot;
>  	opt.priority = cl->priority + 1;

You can remove opt.flags = 0; then :=)

re,
 wh